Radiant tube heater assembly

ABSTRACT

An indirect heater assembly ( 10 ) comprises a radiant tube heater ( 12 ) and a fan ( 14 ) for generating an air flow over the heater ( 12 ). In an preferred embodiment and in another aspect, the radiant tube heater ( 12 ) comprises a radiant tube burner, an elongate tube  16  and a spiral tube ( 23 ) connected to the elongate tube ( 16 ) by a U-shaped tube ( 25 ). The spiral tube ( 23 ) extends around the elongate tube ( 16 ) coaxially thereof.

The present invention relates to a radiant tube heater assembly.

Radiant tube beaters are known, and comprise a burner tube locatedwithin a heater tube. A mixture of fuel and air is supplied to theburner tube where it is mixed, and emerges via a burner head where it isignited so as to produce a flame inside the heater tube. The gas in theheater tube increases in temperature thereby creating a hot tube whichradiates heat to the surroundings. The heater tube includes a fanlocated at one end which draws or blows air along the tube so asdistribute hot air along the length of the tube.

Radiant tube heaters are often used in large volume installations wherethe tube is extended around the installation so that it radiates heatand heats up the surroundings.

One problem with this type of heater is that it is not particularlyefficient for heating locally. For this purpose, conventionalnon-radiant type heaters are used which ignite fuel and air in an opentube so as to produce a flame and heat the surroundings. This type ofheater suffers from safety issues such as having an exposed naked flame,and the fact that the combustion products such as carbon monoxide anddioxide are dangerous and cannot be controlled. Thus using exposed nakedflame heaters is not always desirable, particularly where theenvironment has inadequate ventilation, or where occupants of theinstallation are situated near the heater.

What is needed, is a radiant tube heater which is more suited to heatinglocally, but avoids the safety problems of conventional non-radiant tubetype heaters.

Thus according to the present invention there is provided a radiant tubeheater assembly comprising a radiant tube heater, and air flowgenerating means arranged to generate an air flow over the radiant tubeheater so as to provide convected heating.

Advantageously this provides a flow of hot air to the surrounding areawhich is more easily directed than radiant heat provided by conventionalradiant tube heaters; and heats ambient air rather than surfaces.

Preferably the heater assembly is located within a housing. Thatprevents user contact with the hot radiant tube heater.

The housing preferably has a wall around the radiant tube heater so asto constrain the air flow over the tube heater, the wall defining an airflow pathway over the heater and an outlet to direct the hot air to thesurroundings. That provides an enclosed area in which the air passesmore closely over the heater thereby heating the air more efficiently.The outlet enables the hot air to be directed in a particular direction.

The housing may further include a heating duct which is connected to theoutlet so as to direct hot air to a particular part of the surroundings.

In one embodiment the radiant tube heater comprises an elongate tube.Typically the elongate tube is made from stainless steel to withstandthe high temperatures in the tube. In another embodiment the radianttube heater assembly comprises a spiral tube provided at an end of theradiant tube heater. The spiral tube preferably comprises a straightportion and a spiral portion downstream of the straight portion andarranged around the straight portion, most preferably substantiallycoaxially around the straight portion.

This provides several advantages. Firstly more surface area of heatertube is provided for a given overall heater assembly length, therebyproducing more efficient heating of air. Secondly, since the spiralportion is arranged around the straight portion, air inside the spiralportion is heated by heat radiating from the straight portion of thespiral tube, and thus air passing over the spiral portion is heated moreefficiently.

The radiant tube heater is preferably connected to the straight portionof the spiral tube by a U-shaped tube. The U-shaped tube enables theheater and the spiral tube to be housed in a compact manner. Also, theburner can be held remote from the airflow over the spiral tube whichimproves performance.

The spiral portion is made from a flexible material to enable it to bewrapped around the straight portion.

The straight portion may be connected to the spiral portion by an elbow.

Air flow generating means preferably comprises an impeller to draw airover the radiant heater tube or to blow air over the radiant heatertube. The air flow generating means may be located on the assembly or onthe housing.

The elbow between the spiral portion and the straight portion ispreferably positioned near the air flow generating means. Thus the elbowremains sufficiently cool to prevent damage to the material which istypically not as heat resistant as the stainless steel tube.

Preferably the assembly includes an exhaust duct located in fluidcommunication with the heater tube so as to direct gaseous combustionproducts away from the surrounding environment. More preferably theexhaust duct is located at an open end of the heater tube. This meansthat the exhausted gas is cooler, and avoids exhausting hot gas from thetube which could otherwise be used to heat up the air flow over thetube. Including an exhaust duct is particularly suitable for use with aheater with a spiral tube, since the hot gas has travelled further alongthe tube, and is consequently cooler.

The housing can include wheels located at one or both ends, to enable itto be easily transported within a working environment to wherever heatis required. The use of a spiral tube enables a more compact heater tobe created, and thus makes it easier to transport.

In a preferred form of radiant tube heater a mesh burner head isprovided. Compared to known burner heads, the mesh provides a shorterflame, and thus enables shorter tubes to be used without the end of thetube being impinged by the flame.

Whilst generating a flow of air over a radiant tube heater provides amore effective means of heating surroundings, there are some situationswhere a radiant tube heater is still desirable For example, in a dustyenvironment, a flow of hot air is not particularly welcome. However,known radiant tube heaters either do not produce a sufficient quantityof radiant heat, or to produce enough heat, require a longer tube toincrease the surface area from which heat can radiate. Even when alonger tube is used, the gas inside the tube becomes progressivelycooler as it travels through the tube, and thus an insufficient quantityof heat can be produced.

Another object of the present invention is to provide an improvedradiant tube heater.

According to a second aspect of the present invention there is provideda radiant tube heater, the heater having a heater tube, the tube havinga straight portion and a spiral portion arranged around the straightportion.

The above arrangement provides several advantages. Firstly, more surfacearea of heater tube is provided for a given length of radiant tubeheater, thereby producing an increased surface area to radiate heat.Secondly, since the spiral portion is around the straight portion, airinside the spiral portion of the tube is heated by heat radiating fromthe straight portion of the heater tube.

Most preferably, the spiral portion is arranged substantially co-axiallyaround the straight portion. That means that the spiral portion isheated substantially uniformly by the straight portion.

Several of the preferred features of the first aspect of the inventionequally apply to the second aspect of the invention.

Preferably the assembly includes an exhaust duct located in fluidcommunication with the heater tube so as to direct gaseous combustionproducts away from the surrounding environment. More preferably theexhaust duct is located at an open end of the heater tube. This meansthat the exhausted gas is cooler, and avoids exhausting hot gas from thetube which would otherwise radiate to the surroundings. Including anexhaust duct is particularly suitable for use with a heater with aspiral tube, since the hot gas has travelled further along the tube, andis consequently cooler.

The heater can include means, for example wheels located at one or bothends, to enable it to be easily transported within a working environmentto wherever heat is required. Again, the use of a spiral portion in thetube enables a more compact heater to be created, and thus makes iteasier to transport.

In a preferred form of radiant tube heater a mesh burner head isprovided. Compared to known burner heads, the mesh provides a shorterflame, and thus enables shorter tubes to be used without the end of thetube being impinged by the flame.

The invention will now be described by way of example only withreference to the accompanying drawings in which:

FIG. 1 is a side view of a radiant tube heater assembly according to thefirst and second aspects of the present invention,

FIG. 2 is an end view of the radiant tube heater assembly of FIG. 1,

FIG. 3 is a side cross-sectional view of a known radiant tube heater,

FIG. 4 is a perspective view of part of the radiant tube heater assemblyof FIG. 1,

FIG. 5 is a perspective view of the radiant tube heater assembly of FIG.1 located within a housing, and

FIG. 6 is a side view of a radiant tube heater according to a secondaspect of the present invention.

In FIGS. 1 to 5, a radiant tube heater assembly 10 comprises a radianttube heater 12 and air forcing means in the form of a fan 14.

One example of a radiant tube heater is that described in our co-pendingEuropean patent application EP1217294. The radiant tube heater 12 (FIG.3) comprises a radiant tube burner 14 arranged substantially co-axiallywithin an elongate tube 16. The tube 16 has an external surface 17. Fuelis supplied to a mixing tube 18 via a nozzle 20 which is connected to afuel supply (not shown).

The heater 12 has an orifice plate 22 which includes primary air inletmeans in the form of a first set of holes 24 to supply substantiallyturbulent air to the mixing tube 18, and a secondary air inlet means inthe form of a second set of holes 26 to supply substantiallynon-turbulent air to a second tube 28, the second tube arranged aroundthe mixing tube and having a larger diameter. Air is supplied underpressure by drawing air using an impeller 30 located downstream of theburner. Alternatively air could be supplied by blowing air using a fanupstream of the orifice plate 22. Air and fuel entering the mixing tube18 is mixed upstream of a burner head 32 due to the turbulent air flow.The air/fuel mix emerges from the burner head 32 and is ignited by anignition device 34 to produce a flame. The substantially non-turbulentair emerging from the second tube 28 promotes the long flame shown inFIG. 3. Thus the tube 16 contains hot gas. To withstand the temperaturesof the hot gas, the tube is made from a suitable heat resistantmaterial, for example, stainless steel. Typically the diameter of thetube is 100 mm (four inches).

The assembly includes a spiral tube 23 (FIG. 4) which is connected tothe elongate tube 16 by a U-shaped tube 25. A fitting 27, which is gastight, connects the elongate tube 16 to one end of the U-shaped tube 25.The U-shaped portion has a surface 43.

The spiral tube has an straight portion 29 and a spiral portion 31. TheU-shaped tube 25 is connected to one end of the straight portion by asimilar gas tight fitting 27. The other end of the straight portion 29is connected to the spiral portion by an elbow 33. The spiral portionhas a surface 45 and the straight portion has a surface 47. The elongatetube 16 has a length L which is sufficient to contain the flamegenerated by the burner and prevent the flame from impinging on theU-shaped tube. Typically the straight and spiral portions are 75 mm (3inches) in diameter.

The spiral portion 31 is made from a flexible material to enable it tobe wrapped around the straight portion 29. No combustion takes placeinside the spiral portion 31 and therefore use of high temperatureresistant materials such as steel is not necessary.

The spiral tube is mounted onto a frame 19, and the frame 19 is housedwithin a housing 36. The housing has an elongate hollow cylindricalportion 38 with an outer wall 40, and annular flanges 42 extendingtherefrom. The frame 19 is secured to the annular flanges 42 such thatthe spiral tube 23 and the cylindrical portion of the housing aresubstantially coaxial, and an enclosed space 44 is created between theheater 12 and the housing wall 40.

The fan 14 is positioned at and fixed to an air inlet end 46 of thehousing via suitable fixings (not shown). The fan has a diameter whichis slightly smaller than diameter of the cylindrical portion of thehousing. The fan 14 can be electrically powered, or pneumaticallypowered where it is possible to utilise the air supply used to supplyair to the mixing tube. It will be appreciated that the fan 14 ispositioned near the elbow 33 which connects the spiral and straightportions of the spiral tube and thus the elbow is kept sufficiently coolthereby enabling the use of a material of lower heat resistance.

An air outlet end 48 of the housing has an air outlet in the form of anaperture 50 which is covered by a grill 52. The housing has acylindrical lip 56 extending therefrom. A heating duct 58 ispositionable on the lip 56 so as to direct hot air emerging from theoutlet into the surroundings from its open end (not shown).Alternatively the hot air can enter the surroundings from the aperture50 without the need for a heating duct.

The housing has a rectangular base portion 62, onto which wheels 64locate at one end. A handle 66 is positioned on the base portion at theopposite end. The housing can be manoeuvred using the handle and thewheels and transported to different locations. In other embodiments thehousing may be fixed and not require wheels.

The open end of the spiral portion 31 is connected to an exhaust outlet70 (see FIG. 2) mounted on the outer wall 40 of the housing so as todirect gaseous combustion product from the tube. An exhaust tube 72(FIG. 5) is releasably connected to the exhaust outlet 70, andpositioned such that its open end 74 is remote from the surroundingenvironment, for example; outside of the working environment. Theimpeller 30 is located within the spiral portion at its open end andacts to draw hot gas through the heater tube 16. Thus gas in the hottube passes from the heater tube 16 into the spiral tube via theU-shaped tube, and into the exhaust tube 72 before exiting at its openend 74. Having an exhaust tube which is releasably connected to thehousing is advantageous where the housing is mobile and the exhaust tubeis fixed to the surroundings, for example to an outlet in an exteriorwall.

In operation, fuel and air is supplied to the mixing tube 18 and ignitedso as to produce hot gas in the tube 16. The impeller 30 draws hot gasthrough tube 16 and through the straight and spiral portions of thespiral tube, such that surfaces 17,45,47 become hot. With the fanoperating, air flows in the direction of A into the enclosed space 44,over the hot surfaces 17,45,47 and is heated. The hot air passes overthe heater due to the blowing action of the fan until it exits thehousing via the outlet 50. The hot air enters the surroundings directlyfrom the housing outlet, or where a heating duct is fitted, passesthrough the heating duct where it enters the surroundings at the openend of the duct. Gaseous product from the tube 16 is exhausted viaexhaust tube 72.

It will be appreciated that air passing over the heater is heated inthree ways; by conduction of air adjacent the surfaces 17,45,47, byconvection within the enclosed space 44 as a result of the displacementof cold air which is adjacent the hot air, and by interaction withradiated heat from the surfaces 17,45,47.

In the embodiment of FIG. 1, air is blown over the heater by a fanpositioned at one end of the housing. In another embodiment air could bedrawn over the heater by an impeller located at the opposite end of thehousing.

The embodiment of FIG. 1 uses a known type of burner head. Analternative burner head uses a mesh type material which locates at theend of the mixing tube. The mesh type material interacts with thefuel/air passing through, such that on ignition, a shorter flame isproduced than with conventional burner heads. This enables a shortertube to be used without impinging on the tube, and therefore a morecompact heater assembly.

The embodiment of FIG. 1 relates to a particular example of a radianttube heater. It will be appreciated that the present invention can beused with other radiant tube heaters.

The embodiment of FIG. 1 also houses the heater within a housing. Inother embodiments it is possible to mount the fan onto the assembly andblow hot air over the heater without the need for a housing. Howeveroperation in this way is not as efficient since firstly there is noenclosed space to heat the air, and secondly there is no defined heatoutlet to direct the hot air.

In an alternative embodiment, the radiant tube heater assembly need notinclude the spiral tube extending from the heater tube. In such anembodiment, air would be drawn down the tube by an impeller located atthe end of the tube as opposed to the end of the spiral portion. Theexhaust tube would also be located at the end of the tube.

Operation of such an alternative assembly would be similar to theembodiment of FIG. 1, except in this alternative embodiment the air flowcomes into contact with a smaller tube surface area since there is nospiral tube. Thus to achieve the same heat output it would be necessaryto make the tube of considerable length so as to increase the tubesurface area, which would not be appropriate for a mobile heater.Furthermore, the spiral tube of the tube of the embodiment of FIG. 1 isalso heated by heat radiating from the straight tube, which would not bethe case if only an elongate tube were used. Such an arrangement isappropriate where a lower heat output is required.

In FIG. 6 a radiant tube heater 112 has features similar to theembodiment of FIG. 1 numbered 100 greater.

The heater 212 includes a radiant heater tube 216 as shown in FIG. 1,with a spiral tube 223 which extends from the tube. The heater 212 ismounted onto a frame 219, but in contrast to the embodiment of FIG. 1,the frame is not housed within a housing.

In contrast to the embodiment of FIG. 1, no air flows over the tube.Thus hot gas inside the tubes heats the surroundings by radiating fromthe tubes and not by the heating of air flowing over the tubes.

The housing of FIG. 1 would not be appropriate for this type of heater,as it would form a barrier against heat radiating from the tubes.However, some form of housing, for example a cage 290 could be used toprevent contact with the hot tubes and also allow heat radiating fromthe tubes to enter the surroundings unhindered.

As in the embodiment of FIG. 1, the heater includes an exhaust tube atthe open end of the spiral portion 212 of the heater tube 216 so as todirect gaseous combustion products away from the surroundingenvironment.

This spiral radiant tube heater is advantageous over conventionalelongate radiant tube heaters since the spiral portion provides agreater surface area of tube, thereby enabling a more compact heater tobe produced. Furthermore, the spiral portion enables cooler gas to beextracted by the exhaust tubes creating a more efficient heatingprocess.

It will be appreciated that the features described in relation to theembodiments of FIG. 1 can be included in this embodiment, and hence theheater can include wheels to enable it to be transported, and analternative mesh burner head to generate a smaller flame within thetube. The spiral tube can also be included with other known radiant tubeheaters.

1. A heater assembly comprising: a radiant tube heater, a spiral tubeassembly, and air flow generating means, wherein the radiant tube heatercomprises an elongate tube and a burner within said elongate tube,wherein a fuel is combusted with air and the hot combustion productsflow in a single axial direction along said elongate tube and thenthrough said spiral tube assembly; wherein the spiral tube assemblycomprises a straight portion and a spiral portion, the spiral portionbeing downstream of the straight portion and helically wrapped aroundthe straight portion such that the hot combustion products pass firstthrough said straight portion and then through said spiral portion; andwherein said air flow generating means is arranged to generate an airflow over both the radiant tube heater and the spiral tube assembly,thereby providing a hot air output stream from the heater assembly.
 2. Aheater assembly according to claim 1, wherein the heater assembly islocated within a housing.
 3. A heater assembly according to claim 2,wherein the housing has a wall around the radiant tube heater so as toconstrain the airflow over the radiant tube heater, the wall defining anair flow pathway over the radiant tube heater and an outlet to directthe hot air to the surroundings.
 4. A heater assembly according to claim3, wherein the housing further includes a heating duct which isconnected to the outlet so as to direct hot air to a particular part ofthe surroundings.
 5. A heater assembly according to claim 1, wherein theradiant tube heater comprises an elongate tube.
 6. A heater assemblyaccording to claim 1, wherein the spiral portion is arranged coaxiallyaround the straight portion.
 7. A heater assembly according to claim 1,wherein the radiant tube heater is connected to the straight portion ofthe spiral tube by a U-shaped tube.
 8. A heater assembly according toclaim 1, wherein the spiral portion is made from a flexible material toenable it to be wrapped around the straight portion.
 9. A heaterassembly according to claim 1, wherein the straight portion is connectedto the spiral portion by a suitable joint to provide an airtight seal.10. A heater assembly according to claim 1, wherein the straight portionis connected directly to the spiral portion with no need for a joint,thereby reducing the number of parts.
 11. A heater assembly according toclaim 1, wherein the air flow generating means comprises an impeller todraw air over the radiant heater tube or to blow air over the radiantheater tube.
 12. A heater assembly according to claim 1, wherein the airflow generating means is located close to the connection between thespiral portion and the straight portion so as to cool the connection inuse.
 13. A heater assembly according to claim 1, wherein the assemblyincludes means for removing the products of combustion from the heatertube.
 14. A heater assembly according to claim 13, wherein the removingmeans includes an exhaust duct located in fluid communication with theheater tube so as to direct gaseous combustion products away from thesurrounding environment.
 15. A heater assembly according to claim 14,wherein the exhaust duct is located at an open end of the heater tube.16. A heater assembly according to claim 2, wherein the housing includeswheels located at one or bath ends.
 17. A heater assembly according toclaim 1, wherein the radiant tube heater has a mesh burner head.
 18. Aheater assembly according to claim 1, wherein the assembly includes afresh air inlet duct which supplies air to the radiant tube heater.